Valve actuating mechanism



Feb. 23, 1965 J. DoLzA VALVE ACTUATING MECHANISM 2 Sheets-Sheet 1 Filed Aug. 7, 1965 Feb. 23, 1965 J. DoLzA VALVE ACTUATING MECHANISM 2 Sheets-Sheet 2 Filed Aug. 7, 1963 United States Patent Oiitice lthlilib Patented Feb. 23, 1%65 The present invention relates to a new and improved hydraulic lash adjuster and particularly of the type in which the adjuster mechanism provides a fulcrum for a valve actuating rocker arm. While not necessarily limitedthereto, the present invention relates to a hydraulic lash adjuster which is especially applicable to an overhead valve camshaft engine.

It is the general purpose of the present invention to provide a hydraulic lash adjuster which provides the fulcrum -for a rocker arm, further which includes a selfcontained supply of duid and is, therefore, completely independent of the engine lubricating system.

It has been the practice to supply the liquid used in an hydraulic `lash adjuster from the engine oil system. The use of engine lubricating oil in hydraulic lash adjusters has several inherent undesirable ycharacteristics which have primarily contributed to the malfunctioning of such devices. An hydraulic lash adjuster includes precisionmade parts which coact within closetolerances. In using engine .crankcase oil, whicliisv exposed .to the products of combustionand road`di1t,`it is Vinevitable that the oil eventually contains. impuritieslsuchifs air, gasoline, and dirt particles which unavoidably .iind their way into the hydraulic lash adjusters'." ASuchimpurities# 30 and particles contribute to. the. malfunctining fof "hjyz draulic lash Hadjusters by f deteriorating "parts,i eaiising foaming, andfotherwise inhibiting`the -free movement:cnf`- A fnrther and important probl'eizn'.wlziich occurs in 'hy- 35 draulic Jlash adjuster vsystems .utiliaing-,engine ,lubricating oil results from the fact .that `oil-has range which varies considerably. wiltlit'en'iperaure. otherV words, enginel 4lubricating oiL isfrgelativelyfviscous when the engine is 'cold andfbecoi'nes considrably.less` 40 viscous as engine temperature -iiucreaseanv viscosity variation `creates la serious operatingyproblern draulic lash.adjuster. .5

4lundamentally,'an hydraulic 'lash adjuster includes .aplunger which is closely littedso as to slide asup; port structure wherebywthe length .of the :,idjusterr variable to take up clearances iin the v valve )peratingg.system.V The plunger andV support Armlst be` relatively extensible and yet provide, .in effect, an axially rigid structure in transmitting motion between camshaft .and valve..x This result is achievedby releasably trapping and.; transferring an .incompressiblev fluid :betweenl chambersnim-the ad, juster. `It is apparent that theratefoft'ransferof. such fluid between chambers is greatlygaifectedzjby variathgms55 in viscosity. l Part of thel fluidtransferis occasioned vby leakage between relatively slidable parts.` Therefore, the clearance between these parts has been a compromise between that necessary to accommodate hielt-and thin or Oil. i ji; v

. It is therefore, l.an important objective of the -present invention to provide asealedand independent uid source for each adjuster whereby a lrelatively constant viscosity fluid maybe utilized permitting closer tolerances between parts and a more constant operation of the adjuster.

In the present invention, a unique lash adjuster construction is achieved whereby a completely sealed source of iluid is provided for each adjuster and assumes a more accurate, trouble-free operation than has previously been available in such devices.

It is an important aspect of the present invention that the hydraulic lash adjuster is not associated with the the ynormal functioning'of said adjuster.

other elements of the valve operating mechanism so as to be reciprocab-le with the periodic movement of the camshaft. l'n other words, while the overall length of the adjuster is variable in accordance with changes in size of the various components, duc to variations in ambient operating conditions, the adjuster is mounted as a relatively iixed member so as not to be subjected to reciprocating movement. Reciprocating movement of a hydraulic lash adjuster, as normally occurs when such adjuster is placed in the operative line of movement between a camshaft and -push rod, creates severe operating problems for the adjuster which heretofore has made a sealed system commercially impractical. Rapid reciprocation of an hydraulic lash adjuster creates serious problems of sealing which may fail and cause the loss of the fluid within the lash adjuster.

It is, therefore, an object of the present invention to provide a non-reciprocating hydraulic lash adjuster having a sealed and independent source of fluid which permits the use ,of a relatively stable viscous medium throughout the temperature operating range of an engine.

It is also an important object of the present invention to provide an expandable uid reservoir within the lash adjustei whereby variations in the overall length of the adjster maybe accommodated without creating internal fluid pressures lof a suicient Value to otherwisel upset Other objects and advantages'of the present invention willbe apparent from a perusal of the detailed description taken conjunction the drawings which follow. 4vInhthedrawingsi -.l

URE lis a.v partially verliead valve -camshaft engine embodying the subjectfinvention'.A

FIGUR c 23s a modified form ofthe invention V:shown baSicuyin-.FIGURE- 1.

`FIGURE a farther modieauon" f the banc vDOnln Whichthe axially movable plunger is supported Ya* bracket rnemberrather than lon an inter- I'ediate stud member. i .f

FIGURE 4 isa modification of the form of invention shownin FIGURE 3.

f FIGURE 5. is af `*ther modication of the invention'.A

.Referringto .FIGURE l of .the drawings, an engine cylinder Vhead is indicated generally at 10 and includes:

a.,va1 ve..member 12 reciprocably disposed therein. For purposes of the present invention, valve ,1 2 may be either an inlet or an`exhaust valve and .is biased into-aclosed position by a'coiled .spring 14 disposedl between the cylinder head anda retainer washer 16 fixed to the upper end of valve stem18. v f .w.

.While thepresent invention is not rlimited to an engine construction .inA which the camshaft 20 is disposed overhead, vit is'partcularly useful with this type of. engine.l In other Words, the camshaft may be disposed jin the lower portion ofthe cylinder block .with its motion'being transmitted to rocker arm 22 through a push rod. However,` in the engine with which the subject invention is illustrated, rocker arm 22 includes arcuateends 24 and 2d which coact respectively with valve stern-18 and camshaft 20. Y

Anhydraulic valve lash adjuster is indicated generally l at 28 and is supported upon a xed bracket member 30 securedto or formed integrally with cylinder head 10. In the modilication of FIGURE 1, lash adjuster 28 includes a stern member 32 pressed within a corresponding opening formed in bracket 30 and locked therewithin by a split ring retainer 34. The lower end of stem 32 projects considerably below bracket 30 so as to provide clearance for Islidably receiving a cylindrical sleeve plunger member 36 which is open at its upper end and termisectioned elevational view of nales in closed arcuately shaped portion 3S at its lower end. The arcuate or bearing end 33 oi slidable plunger 36 is adapted to coact with a correspondingly shaped bearing portion 4# formed on rocker arm Z2.

Stern 2 includes a coaxially extending passage 42 which communicates at its lower end with a cham er 44 formed by the stem land slidable plunger member 36. The other end of passage 42 communicates with diametrically extending passage A exible diaphragm seal member 48 includes annular bead portions 5t) and 52, which respectively coact with stem E2 and the upper end of plunger 36 to dene an expandable or variable capacity chamber 54.

A perforate cage member 56 includes a flange portion 58 biased by a coil spring 6@ against a radial shoulder 62 formed proximate the lower end of stem member 32. The other end spring 69 biases against the inner surface of the arcuate end 38 of slidable plunger 36. Cage 56 includes an inwardly oset tab 64 which 4supports a disc member 66 in an off-center relationship whereby the disc operates as a valve to admit Huid to chamber 44 when plunger 36 moves downwardly away from stem 32 and closes when the movement of the plunger is in the opposite direction.

Chambers 44 and 54, as wellas passages 42 and 46,

constitute a sealed reservoir and are adapted to be filled with a suitable iiuid whereby the overall length of the adjuster may be varied by relative movement between plunger 36 and fixed stem 32 such that rocker arm ends` 24 andA 26 m-ay be maintained at zero clearance with respect to'valve stem 18 and camshaft 20.

AAs' already noted, crankcase oil is used for normalv engine lubrication purposes and-is continuously suppliedto present commercial hydraulic lash adjusters.. This oil is relatively unstable from the point of view of viscosity. On the'other hand, oils or related tluids which are relatively viscosity-stable are relatively expensive andnot necessarily suitable for the lubrication of. high-loadem,

gine parts. Thus, under cold starting conditionsihydraulic lash adjuster supplied withcrankcasefoil is apt -to be-relaitivelystiif operating, causingadjuster operaiiont' lag behind clearance requirementsofthe valve operating mechanism in maintaining the aforementioned zero clearance non-lash coaction of thee'rocker arm with the camshaft andvalve stem. As a result, for alimited'timeafter starting the engine, clearance may develop between these members, causing the valve operating mechanism to knock Since the present invention provides a construction in Whichthe huid contained in 'each of the lash-adjustersl is independent of and isolated from the 'general engine lubricating-system and further'jinwhich limited quanti-Y ties of fluid are required, a more` viscosity-stable liquid" may be utilized. For instance, the subject hydraulic lash adjuster has been designed to permit the use of a silicone liquid which has high viscosity stabilitythroughout the engine temperature operating range. Consequently, without senies viscosity fluctuations, .the relatively slidable surfacesof the adjuster may be more economically manufactored to tolerances that will permit the desired amount of leakage under the full range of operating conditions.

In operation, when it is necessary for the relativeA length of the hydraulic adjuster to be increased to *maintain the aforementioned non-lash coaction between the various valve operating members, spring 60 will urge the slidable plunger member 36 downwardly whereby a uid pressure diilerential is created across valve 66 causing the same to open and admit a limited quantity of uid vertical force on slidable plunger 36. Such force will.

maintain duid in chamber 44. under sufficient pressure to cause the same to leak between the plunger and the stem and thereby How into the expandable chamber 54.

Since disc valve 66 is maintained, closed circulation of the uid in the system is prevented and the displaced liquid volume is accommodated by the llexure ofseal 4S. As aresult, the overall length of adjuster '28 is shortened as spring 14 moves valve 12 to a closed position; After valve 12 becomes seated against cylinder headv 10, ad-

juster spring 60, acting in the opposite direction to valvev spring 14,k will maintain the rocker arm :in vabutting engagement with the valve and camshaft'.

The simplicity ofl construction of adjuster 28 results in a device' which, notwithstanding the'4 normally `greater cost of adjuster uid, is at least no vmore expensive than present valve lash compensating devices and does achieve signicant functional improvements.

To further reduce the cost ofthe subject type, lash-v adjuster, it is possible to utilize two uids of' different specilc` gravities for avcomposite adjuster uid. Tovillus-' trate, thefloweriportionofstem passage 42 may be filled' passage, "as ,wellas ','diameualpassageflt Vand' expansible' chamber 54 I maybe: lilledlwith'a conventionall lubricating oil 70.' 'The lubricating oilinthe'upper 'portion of the reservoirwould be of a lower specic `4gravity than the l silicone liquid and, therefore, duid would remain ,stran'ed with the silicone'onthebottom and the oil oirtlnj;Y top.

Even during operationof the adjusterwith'theleakage ofk the sliconejliquidbetween the'plungerand'the stem, thej heavier` siliconeliquidlwill pass underneath the'lighter j @i1 maturato me maanas sf ,the-'Sem passage.

from passage 42 into chamber 44 until the rocker arm portions 24 and 26 respectively engage valve stem 18 and camshaft 2?. As the valve mechanism operates, a limited amount of leakage of the fluid in chamber 44 will occur between the inner Wall of plunger 36 and the outer Wall of stem 32 whereby such duid will ow upwardly into the chamber Se and hence inwardly through throughout thadjusti; its lesser' viscositf'stability in relation to the silicone ud has no adverseetfecton the functioning of the adjuster. Further',`a1id;to-gthe extent thata limited ,amount ofthe oil might'becine exposedtothe croactingjs'urfaces ofthe plunger steimthe lul-iril cation of? thesepar'ts vvvouldr be 'improved since such oil is normally a betterlubricant than is 'they silicoeuid.

, the eventfthatocker rmp22 tends'toiotateaboutV the longitudinal faxisfof vtheadjuster, ai'guidemember 72 may beprovided.n 'Guide member'7,2"includesv a downwardly extending? portion 74 which is? bifurcated'or vsplit f at its lowerend so as to straddle'a ribi76 on'the rocker arm. In this manner vthe rocker arm 2 2lislpositi`vely restrained against the vaforesaidrotary movement.-

FIGURE 2 representsa modied form of the invention shown in FIGURE l wherein basically-tlie-'same combination of elements :is utilizedand including' support 78, a

fixed stem 80, and a plunger 82. In this modiiication,V

a bellows-type expandable member-84 is-utili'zedin place of the exible diaphragm'member 48'shown in FIGURE 1. Bellows-84 may be formed of metal, plastic, or an elastomeric material which is unaiected by exposure to the fluids used in and outside the adjuster.

In the modifications of both FIGURES 1 and 2, the side thrust forces imposed by the actuation rotating camshaft 20 are transmitted by the plunger supporting stem to the support member 30 or 78.

Reference is now made to the modication of FIGURE 3. Plunger 86 is..slidably mounted directly within xed Plunger 86 includes a radially relieved portion 92 formed near its upper end and which generally coacts with a radially reduced stem portion 94 of plug 90 to dene an annular chamber 95 enclosed by a liexible sealing member 96. Both the plunger and plug include annular recesses 98 and 100 adapted to receive the annular lips 102 and 104 of the iexible seal member whereby the latter is retained within the adjuster assembly. To insure retention of the seal within the assembly, an outwardly expanding spring member 105 biases the seal lip 102 into engagement with the plunger and an inwardly biasing member 108 secures lip 104 to the plug. It is to be noted that the seal lips 102 and 104 are proximately disposed relative to the longitudinal axis of the adjuster so as to form a thin U-shaped portion 110 therebetween. U- shaped seal portion 110 depends Within chamber 95 for purposes which will subsequently be described..

The lower end of plunger 86 is again spherically formed to provide the fulcrum support for a rocker arm, as shown in FIGURE l.

Plug 90 includes a passage 112, communicating chamber 95 with a chamber 114 vformed by theplug, and plunger 86. A ball valve member'116 is adapted to control -uid flow between ,chambers 95 and 114. The ball member is confined bya perforate retainer member 118 which is biased against the bottom end ot plug 90,by a coiled spring 120. 'I'he other end of spring 1 18 seats against the inner end of plunger 86 and provides a downward-or extending bias to the plunger to facilitatethe zero' lash or clearance relationship between the rocker arman'd the coacting valve and camshaft members, supra Again, kthe Aliexiblelseal member"96 Lencloseis sealed hid'rese'rvoir Acomprised gf chamber 95, .plug passage l112, and chamber 114. The reservoir is filled with a viscositvstable `liuid, .Suchas the silicone discussed, ,'35

whereby asiplu'nger 86 is caused to'moveaxiallydovvng` wardlyto increase the 'overall lengthofthed v valve 116 will open to permit yfluidtci flow intqchamber ,t 114. During'operationfoff the valve actuating system, a limited mountfof uid will 1eakfrom}chamber `114 b'e-,r

tween plunger 1861vand`plug',90f`intfcliamber 95 to be' adjusteristo remain 'the orbeincreased.

',Under operation conditionscausing a dimurtion overallllength of the adjuster, i-.e. upward-movement of tlieiiplunger, uidleki'ng 4into chamber195 will be re' tained therein. It is apparent 'that as the volumeof charn- 4 ber 114 is diminished, chamber 95 must experience a corresponding increase in volume. This increaseY in volume of the upper or storage chamber is achieved` through radial collapsing, inward and outward, ofthe U-shaped portion 110of seal 96. A f; 1 j

Accordingly, the total sealed liuid'volume of the 'adjuster remains constant eventhough the volume of chambers 95 vand-'114-va1'y' insaccordance with the axial'position of plunger 86re1ative to both support 88 and plug 90.

vOne ofthe diicultes in providing a-'sealed fluid system for a lash adjuster .is.to insure..a transfer of fluid from the compression chamber 114proximaterthe fulcrum end of the adjuster, andthe storage or,.reservoir chamber 95 proximate the upper end of the plunger, without creating internal fluid pressure forces which will adversely affect adjuster operation. To illustrate, spring 120 urges the upper end of plug 90 into engagement with retaining disc 122. Accordingly, there is a resultant downward force urging plunger 86 in an extended direction. With the reservoir chamber at its maximum volume, as when the plunger is fully retracted, a taut sealing member would create an upward force on the plunger thereby diminishing or even overcoming the plunger-extending action of spring 120.

Ideally, exible seal 96 should have no etfect whatsoever on the functioning of spring 120. To achieve this result, seal 96 is made in a distinct bellows or pleated form whereby changing volumes of reservoir chamber 95 cycled back into thejformer chamber if, the length ot.the,

are accommodated by the expansion or collapsing of the Walls of U-shaped seal portion 110 rather than through a stretching or tensioning of the seal member. Consequently, fluid induced deformation of seal 96 occurs without the creation of excessive forces which might otherwise tend to interfere with the control of plunger movement by spring 120.

In this modification of the invention in which plunger 86 directly slidably engages support member 88 rather than being mounted on an intermediate stem member, a distinct advantage is realized in that the vertical overall length of the adjuster may be considerably diminished. At the same time in this modification it becomes necessary to assure that the coacting surfaces between plunger 86 and support member 88 are lubricated. Such lubrication may be left to the normal splashing of rocker arm lubricant on the plunger which will, in turn, be carried up to support 88. As an alternative, engine lubricant may splash .on top of retainer disc 122, which can be perforated to permit the loil to drip downwardly between the support and the plunger. A further alternative is to providefan oil passage 124 in support 88 which is supplied with engine lubricating oil to provide for proper lubrication of the plunger.

It is to be appreciated that the internal lubrication ofl plunger 86 and plug 90 will be achieved through the normalcirculation of the sealed liuid as already described.

1The modification of FIGUREy 4` varies v,only slightly fromwthat of I `IGUR.` Ei-3.A In this/case, the inner plug member is' of a tubular construction comprising an upper portion' 12H5'and a lower portion 1276. Ports- 128 are formed in portion 125 tocommunicate the interior of the plugfyvith reservoir chamber 130.- n u y.

e ger .132'1'ncludes Aarnannular groove 134 formed Pt 1-mte.the` uppertendffhereof and into which ts an- .nular bead 136 of seal 138. ;'I`l1us, the lower end of the Vseal is retained between plunger i132 and xedsupport 140mt Y.

are eliminated.

It fisfalso intended that the pleated orV otherwise formed with an excesswofmaterial whereby the seal may freelypexpa'nd without'creating any in accordancewith the pressures within the assembly. v

In the modilicationshown -in,FIGURE 5, the various elements arearranged in such away thatfthe hydraulic lash adjuster. and the valve member coact'with the ends ofztheroclrer arm and the camshaft actuates said arm intermediate the ends thereof. v

Referring specifically to FIGURE ac ts with the spherical end y24 of rocker arm 22 while the hydraulic lash adjuster 28 coacts with the other end26. In'this ,instance, both the valvemember, and ,lash adjuster aredisposeduon the same side of the rocker 1v Camshaft 20 coacts with the intermediate-portion of rocker arm 22 and is disposed on the opposite side thereof relative to the valve and lash adjuster.

Lash adjuster 28 is mounted in a stationary support 146 and includes a hollow plunger 148 including a closed end having a spherical portion 150 and an open end. A plug 152 is disposed within the hollow plunger 148 so that the plunger and plug are relatively slidably related. Plug 152 includes a diametrically reduced portion which forms a stem 154 adapted to bottom Within support 146. As in FIGURE 3, plunger 148 and plug stem 154 are suitably formed to receive adjacently disposed annular beads 156 and 158 of U-shaped liexible seal member 160. Once again, the plunger 148, plug 152, and seal 160 coact to form a variable volume uid chamber 162. Reservoir 162 is communicated through a plug passage 164 with a yheeridiof .a :smaller diameter y beadl142 which snaps` over a button l144 formed on plugportion 125., In this form of adjuster seal spring retainers second variable volume chamber 166 formed by the closed end of plunger 148 and the adjacent end of plug 152. Ball checl` valve member 168 disposed in chamber 166 permits the contained fluid to ow from chamber 162 t chamber 166 but prevents the reverse tiow. Ball member 16S is maintained in position by a retainer member 17) and a spring member 172 which normally biases the valve to a seated position.

A spring member 174 is disposed in chamber 166 t0 maintain retainer 170 against plug 152 and biases plug 152 and plunger 148 in axially opposite directions.

A third fluid chamber 176 is detined by support 146, plunger 148, plug 152 and seal 166. Oil from the engine lubricating system may be supplied to chamber 176 through passage 178. In some cases it is desirable to provide means to facilitate flow of fluid from the reservoir chamber 162 to chamber 166 in order to assure prompt response to a need for lash take-up. To this end, engine lubricating oil in chamber 176 will create a pressure on seal diaphragm 160 which, in turn, pressurizes the uid contained in reservoir chamber 162. In thus pressurizing the contained fluid, the pressure drop across valve 168 is also increased whereby movement of plunger 148 away from plug 152 will cause a prompt ow of uid into chamber 166 diminishing the likelihood of cavitation which otherwise occurs when fiuid flow into said chamber lags behind plunger extension. It will be appreciated that the problem of cavitation can become particularly severe when the contained uid is very viscous as when the engine is cold. The problem of cavitation is thus greatly diminished by the lluid pressure created in chamber 176.

The oil in chamber 176 is sealed from the contained fluid in chambers 162 and 166 by seal 160. In addition, the oil in chamber 176 provides the lubricant between plunger 148 and support 146.

I claim:

1. An hydraulic lash adjuster device comprising a fixed support, a hollow plunger member slidably supported within said support, said plunger including an open end and a closed-end formed to provide a spherical seat, a

stop member disposed within said support and adapted to limit the axial movement of said plunger within said support, a plug member disposed within said plunger member and including an end portion projecting through the open end of said plunger, spring means urging said plug into engagement with said stop member and also urging said plunger axially away from said support and said plug member, the closed end of said plunger and said plug forming a first variable volume fluid chamber, an expandable seal member including a first portion secured to the plunger proximate the open end thereof and a second portion secured to said plug whereby said plunger, plug, and expandable seal define a second variable volume fluid chamber, passage means formed through said plug member and communicating said first and second fluid chambers, and a valve member coacting with said passage means to permit flow from said second to said first uid -chamber and preventing oW from said first to said second chamber.

2. An hydraulic lash adjuster device as set forth in claim 1 in which sufiicient clearance is provided between the relatively sliding surfaces of said plunger and said plug to permit. a limited fiow of fluid from said first to said second chamber when said plunger is moved toward said ixed support.

3. An hydraulic lash adjuster comprising a hollow plunger open at one end and closed at the other end, a member with which said plunger slidably coacts in a telescoping relationship, the closed end of said plunger and said member defining a first variable volume fluid chamber, an expandable seal coacting with said plunger and said member to define a second variable volume uid chamber, a constant volume of fluid filling said chambers and sealed within said adjuster, said fluid including a first liquid having substantially constant viscosity through the ambient temperature operating range of the adjuster and a second lubricating liquid of less specific gravity than said first liquid, and valve means for controlling uid flow between said chambers as said plunger slides relative to said member.

4. An hydraulic lash adjuster comprising a hollow plunger open at one end and closed at the other end, a member with which said plunger slidably coacts in a telescoping, relationship, the closed end of said plunger and said member defining a first variable volume uid chamber, an expandable seal coacting with said plunger and said member to define a second variable volume fluid chamber, means biasing said plunger axially away from said member, first and second passage means interconnecting said chambers, said second passage means being formed by limited clearance between the slidably coacting surfaces of said plunger and said member, a one-way valve coacting with said first passage means to permit uid to ow from said second to said first chamberV as said plunger movesV axially away from said member, and a uid including a first liquid having substantially constant viscosity throughout the ambient temperature operating range of the adjuster, and a second lubricating liquid of less specificgravity than said first liquid, said first liquid being primarily contained in said first variable volume chamber, said second passage means being restricted whereby as said plunger is moved toward said member fluid will-leak through said second passage means from said first to said second chamber.

References Cited'in the file of this patent UNITED STATES PATENTS Sampietro July 24,

UNITED STATES PATENT OFFICE CERTIFICATE OF CURRECTION Patent No. 3,170 ,446 February 23, 1965 John Dolza 1t is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 58, for "series" read serious Signed and sealed this 3rd day of August 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Ufficer Commissioner of Patents 

1. AN HYDRAULIC LASH ADJUSTER DEVICE COMPRISING A FIXED SUPPORT, A HOLLOW PLUNGER MEMBER SLIDABLY SUPPORTED WITHIN SAID SUPPORT, SAID PLUNGER INCLUDING AN OPEN END AND A CLOSED END FORMED TO PROVIDE A SPHERICAL SEAT, A STOP MEMBER DISPOSED WITHIN SAID SUPPORT AND ADAPTED TO LIMIT THE AXIAL MOVEMENT OF SAID PLUNGER WITHIN SAID SUPPORT, A PLUG MEMBER DISPOSED WITHIN SAID PLUNGER MEMBER AND INCLUDING AN END PORTION PROJECTING THROUGH THE OPEN END OF SAID PLUNGER, SPRING MEANS URGING SAID PLUG INTO ENGAGEMENT WITH SAID STOP MEMBER AND ALSO URGING SAID PLUNGER AXIALLY AWAY FROM SAID SUPPORT AND SAID PLUG MEMBER, THE CLOSED END OF SAID PLUNGER AND SAID PLUG FORMING A FIRST VARIABLE VOLUME FLUID CHAMBER, AN EXPANDABLE SEAL MEMBER INCLUDING A FIRST PORTION SECURED TO THE PLUNGER PROXIMATE THE OPEN END THEREOF AND A SECOND PORTION SECURED TO SAID PLUG WHEREBY SAID PLUNGER, PLUG, AND EXPANDABLE SEAL DEFINE A SECOND VARIABLE VOLUME FLUID CHAMBER, PASSAGE MEANS FORMED THROUGH SAID PLUG MEMBER AND COMMUNICATING SAID FIRST AND SECOND FLUID CHAMBERS, AND A VALVE MEMBER COACTING WITH SAID PASSAGE MEANS TO PERMIT FLOW FROM SAID SECOND TO SAID FIRST FLUID CHAMBER AND PREVENTING FLOW FROM SAID FIRST TO SAID SECOND CHAMBER. 